The present invention relates to preferential heating of materials by non-ionising electromagnetic radiation.
The term "non-ionising electromagnetic radiation" is understood to include, by way of example, microwave radiation and radio wave radiation.
One particular, although by no means exclusive, use of the present invention is to preferentially heat micro-organisms to temperatures that destroy the micro-organisms.
This use of the present invention has a large number of applications.
One application is the medical industry in which the invention may be used, by way of example, to sterilise pharmaceuticals, packages for pharmaceuticals, and surgical and other equipment and implements.
Another application, which is of particular interest to the applicant, is the food processing industry.
The term "food processing industry" is understood to cover industry involved in preparing and packaging food products, including solid and liquid food products.
It is a critical requirement of the food processing industry:
(i) to sterilise food products after the food products have been packaged; or PA1 (ii) to prepare and thereafter package food products under sterile conditions. PA1 (i) chemical sterilisation, such as hydrogen peroxide and chlorine; PA1 (ii) UV radiation; PA1 (iii) gamma radiation; and PA1 (iv) steam sterilisation.
One example of the first category is the widely used method of packaging beverages, such as beer, which comprises pasteurising the beverages. Typically, suitable packaging (such as metal or glass containers) is filled with the beverages, the packaging is sealed, and the packaged beverages are thereafter heated at a temperature of 65-70.degree. C. for 15 minutes. This method, whilst effective, has a number of disadvantages including substantial capital and operating costs.
Another example of the first category is the known method of sterilising spices. Typically, suitable packaging is filled with spices, the packaging is sealed, and thereafter ethylene oxide is permeated through the packaging at high pressure and contacts and destroys micro-organisms on the spices. While ethylene oxide is an efficient means of destroying bacterial spores and other micro-organisms carried by the spices, it is toxic and therefore removal of residual ethylene oxide to low levels is critical. Inevitably, this involves careful control of the method which in turn increases operating costs.
An example of the second category is packaging beverages under aseptic conditions.
Typically, beverages are prepared and conveyed to a filling station under sterile conditions, the filling equipment is maintained under sterile conditions, packaging is sterilised and transported to the filling station under sterile conditions, and the beverages are filled into the packaging and the packaging is sealed under sterile conditions.
An important factor in aseptic packaging of food products is the sterilisation of the packaging.
Known technologies for sterilising packaging in the food processing industry include:
There are advantages and disadvantages with each option and the suitability of these (and other) technologies in any given situation depends on the packaging, the food product, and the food preparation.